1. Field of the Invention
The present invention provides a process for beneficiation of iron oxide-containing titaniferous materials by electrolysis in molten salt to produce iron and high-grade TiO.sub.2.
2. Description of the Prior Art
Titaniferous materials, such as ilmenite, which contain iron oxide are used as feed in the chloride process for making TiO.sub.2 pigment and Ti metal. In the chloride process iron and other impurities are chlorinated with the titanium, causing excessive chlorine consumption as well as a problem of iron chloride waste disposal. It is desirable to have an economic process to remove iron from titaniferous materials before their use as feed in the chlorinator.
British Patent 1,530,806 discloses a process for beneficiating ores containing metallic values in the form of refractory oxides and pyrometallurgically reducible metallic compounds. The ore is subjected to pyrometallurgical reduction to produce a metal-refractory oxide composition, the metallic portion of the composition being the reduced product of the pyrometallurgically reducible metallic compounds. The metal-refractory oxide composition is then subjected to electrolysis in an aqueous medium to solubilize at least a major part of the metallic portion of the composition, and recovering a refractory oxide product from the electrolytic cell. This process is applicable to titaniferous ores, and in another embodiment, the reduced ore may be used as a soluble anode where TiO.sub.2 is recovered at the anode, and Fe at the cathode. Similar processes in which reduced iron-containing titaniferous ores are electrolyzed in aqueous mediums to yield Fe as pure as 99.9%, and a beneficiated TiO.sub.2 product containing greater than 90% TiO.sub.2 have also been disclosed by: Cunningham, G. L. and Pretka, F., U.S. Pat. No. 2,852,452 (1958); Allan, B. W. U.S. Pat. No. 3,941,668 (1976); Jain, S. K. and Jena, P. K., Trans. Soc. Adv. Electrochem. Sci. Technol. 11(4), 481-5 (1976); Allan, B. W., Ger. Pat. DE 2,557,411 (1977); Mori, et al., Japan Patent JP 52,128,817 (1977); Pandey, et al., Res. Ind. 22(2), 77-9 (1977); Allan, B. W., Japan Patent JP 60,033,769 (1985);
U.S. Pat. No. 4,637,865 discloses a process for extracting a metal from a source material containing the metal. The source material is leached with an aqueous solution containing an N-halohydantoin compound to produce an aqueous leachate containing the metal which is then recovered by electrodeposition.
U.S. Pat. No. 4,272,343 discloses a process for beneficiating ilmenite ore using electrolytic reduction. The ilmenite ore is mixed with an acidic solution and the mixture is electrolysed to reduce at least some of the ferric iron to ferrous which dissolves in the acidic solution. It is mentioned in column 2, lines 7-11, that potentiostatic control in the electrolysis is preferred over constant current or constant voltage conditions, since the working electrode can be maintained at the optimum potential versus a reference electrode for the reduction of the iron in the ore. In the electrolytic cell the acidic leaching solution comprises the catholyte which is separated from the anode and anolyte solution by a diaphragm. The leach liquor is separated from the beneficiated ore by filtration, centrifugation or the like.
U.S. Pat. No. 4,047,934 discloses a process for removing iron from an oxide-containing material comprising iron oxide in the presence of a non-ferrous metal oxide. The oxide-containing material is heated with a solid carbonaceous material in a molten salt bath at a temperature or 750-1300 degrees Celsius; the salt bath comprising at least one chloride selected from the group consisting of alkali metal chlorides and alkaline earth metal chlorides, and optionally contains a hydrogen chloride generator. The iron oxide in the oxide-containing material is selectively reduced to iron while leaving non-ferrous metal oxide substantially unreduced. The salt enhances segregation of the iron from the oxide.
Madkour, et al., J. Electroanal. Chem. Interfacial Electrochem., 199(1), 207-210 (1986) disclose a method for the electrowinning of Ti and TiO.sub.2 from ilmenite ore. The mother liquor used for electrolysis was produced by direct leaching with H.sub.2 SO.sub.4 or by the fusion method using NaOH or Na.sub.2 S.sub.2 O.sub.7 as fluxes at 700 degrees Celsius. The Ti and TiO.sub.2 were deposited on platinum sheet cathodes. Several baths suitable for the electrochemical extraction of Ti and TiO.sub.2 from ilmenite are given. Only the oxalate bath is suitable for recovery of TiO.sub.2.
U.S. Pat. No. 4,165,262 discloses a method of electrolytically producing Ti metal by introducing an ionisable Ti compound into a molten salt bath in the cathode compartment and impressing an emf to form gas at the anode and deposit Ti at the cathode. The preferred titanium source is titanium tetrachloride, and the preferred salt is a eutectic mixture of LiCl and KCl. Other disclosures related to the electrolytic production of Ti metal from a titanium halide melt or a molten salt containing titanium ore are given in: U.S. Pat. Nos. 4,118,291; 4,082,628; 3,777,012; 3,711,386; 2,921,890; 2,757,135; and French Patent FR2,359,221 A.
U.S. Pat. No. 4,563,338 discloses a process for selective chlorination of a simple or complex mixture of metallic oxides containing at least one element to be recovered chosen from Fe, Ti, Al, and Si together with accompanying impurities. The process comprises milling and calcining the starting material, suspending the material in a molten salt bath, and introducing chlorinating agents into the bath. The bath should be maintained at a temperature sufficient to ensure that at least one of the metallic chlorides formed volatilises. Selective extraction of the chlorides formed is achieved by successive introduction of specific chlorinating agents of increasing chlorinating power, in a number at least equal to the number of vaporisable elements to be recovered. The process is useful for among other things, ilmenite ores. A related report is given by Tremillon, et al., NATO ASI Ser., Ser. C, 202 (Molten Salt Chem.), 305-27 (1987).
U.S. Pat. No. 4,460,550 discloses a process for producing titanium tetrachloride from titanium ore and reductant suspended in molten salt, at a temperature between about 800 degrees and 1000 degrees Celsius, by passing chlorine through the melt. The salt may be NaCl, KCl, CaCl.sub.2 or their mixtures. The reductant is preferably coke. A similar disclosure is given in U.S. Pat. No. 4,442,075. Other disclosures related to molten salt chlorination of titaniferous ores are given in: Murphy, A. H. U.S. Pat. Nos. 4,518,426 and 4,487,677; Mukliev, et al., Soviet Patent SU-956,588; Ferry, et al. Trans. Instn. Min. Metall. (Sect. C: Mineral Process. Extr. Metall.) 97, p. C21 (1988); Akashi, et al., Nippon Kogyo Kaishi 86(989) 553-8 (1970); Egami, et al., Nippon Kogyo Kaishi 86(992), 871-6 (1970).